Fuel control system for internal combustion engines

ABSTRACT

A fuel control system for internal combustion engines comprising a first control signal generator to produce an output voltage corresponding to an operating parameter of the engine, and a signal processing circuit including a non-linear means for deriving from the output voltage of the first control signal generator a plurality of voltages having non-linear relation with the output voltage of the first control signal generator, which are adjustable to provide for a plurality of slopes corresponding to respective subdivided portions of the fuel demand characteristic of the engine, and an amplifier-adder to amplify and add together the derived voltages so as to produce a total output voltage conforming to the engine fuel demand characteristic over the entire range of the engine-operating parameter. The pulse width of the pulse signal to energize the fuel injection valves is varied in accordance with the total output voltage from the signal processing circuit. Thus, even if the fuel demand characteristic is non-linear, it may be closely followed over the entire range of the involved engine-operating parameter in controlling the amount of fuel supplied to the engine.

United States Patent [191 Wakamatsu et a1.

[11] 3,817,226 1*June 18,1974

COMBUSTION ENGINES Endo, Anjo, both of Japan [73] Assignee:

Notice:

patent subsequent to Sept. 19, 1989 has been disclaimed.

Filed:

Appl. No.: 284,547

1970, Pat. No. 3,692,003.

References Cited UNITED STATES PATENTS Beishir...

FUEL CONTROL SYSTEM FOR INTERNAL Assistant Examiner-Cort Flint Inventors: Hisato Wakamatsu, Kariya; Kunio Nippondenso Co., Ltd., Kariya-shi, Aichi-ken, Japan flieiioriion'oitiie test of this Attorney, Agent, or FirmCushman, Darby & Cushman [57] ABSTRACT A fuel control system for internal combustion engines comprising a first control signal generator to produce an output voltage corresponding to an operating parameter of the engine, and a signal processing circuit including a non-linear means for deriving from the output voltage of the first control signal generator a US. Cl. 123/32 EA, 123/119 R, 123/140 MC Int. Cl. F02m 51/06 Field of Search 123/32 AE, 32 EA, 139 E,

Baumann 123/32 EA 123/32 EA Suda 123/32 EA Schlimme 123/139 E Wakamatsu 123/32 EA plurality of voltages having non-linear relation with the output voltage of the first control signal generator, which are adjustable to provide for a plurality of slopes corresponding to respective subdivided portions of the fuel demand characteristic of the engine, and an amplifier-adder to amplify and add together the derived voltages so as to produce a total output voltage conforming to the engine fuel demand characteristic over the entire range of the engine-operating parameter. The pulse width of the pulse signal to energize the fuel injection valves is varied in accordance with the total output voltage from the signal processing circuit. Thus, even if the fuel demand characteristic is nonlinear, it may be closely followed over the entire range of the involved engine-operating parameter in controlling the amount of fuel supplied to the engine.

4 Claims, 7 Drawing Figures SAW-TOOTH PULSE FUEL FUEL WAVE SIGNAL INJECTION INJECTlION \T I-TGENERATOR- GENERATOR VALVE DRNE VALVE 5\ "5 1 FIRST SIGNAL 0 1 1 11 -'s|e-A| PROCESSING v o G R/n'm SECTION 2\ SECOND 4 SIGNAL GENERATOR THIRD SIGNAL GENERATOR I SIGNAL FROCESSING PATENTEIIJIIII I8 mm A 3,817" 22 sIIT1 0r 4 FIG v l.

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\ SAW-TOOTH PULSE FUEL FUEL l; wAvE -+.SIGNAL INJECTION INJECTION GENERATOR GENERATOR AL E VALVE FIRST SIGNAL 4o 14DI4G 14d GENERATOR SECTION 2\ SECOND 4 SIGNAL GENERATOR THIRD SIGNAL GENERATOR FIRST SIGNAL GENERATOR sIIIIi GENERATOR Pmmmwmm 3817.226

SHEET 3 4 I FIRST SIGNAL GENERATOR SECOND SIGNAL GENERATOR THIRD I SIGNAL GENERATOR pmmznmwm I 381TL226 sum g or 4 FIG. 7

FIRST SIGNAL W. IO

s I SECOND I I SIGNAL 'wwvm,

GENERATOR 3 THIRD I I SIGNAL wwvvv- GENERATOR i FUEL CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINE CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 54,681 filed on July 14, 1970 now US. Pat. No. 3,692,003.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to fuel control systems for internal combustion engines for controlling electromagnetically operated fuel injection valves in accordance with operating parameters of the engine.

2. Description of the Prior Art The fuel control system of the type pertaining to the invention usually uses an electromagnetic feedback type multi-vibrator consisting of a-pair of transistors and a feedback transformer to provide for the feedback from the collector of one transistor to the base of the other transistor of the multi-vibrator. The amount of feedback, that is, the mutual inductance of the feedback transformer is varied in accordance with the negative pressure in the engine suction pipe, which is one of the engine operating parameters, thereby varying the pulse width of the pulse output of the multi-vibrator which faithfully follows the fuel demand characteristic of the engine. The pulse output is impressed on the fuel injection valve to drive it in such a manner that it is held in the operative or'open position for a period equal to the pulse width, during which the fuel is injected either into the intake manifold of the engine or directly into the cylinder.

As the means to vary the mutual inductance of the multi-vibrator in accordance with the engine intake negative pressure is used a movable iron core coupled to a diaphragm converting the change in the intake negative pressure into a corresponding mechanical displacement thereof, whereby the'associated motion of the movable iron core produces variation of the mutual inductance of the multi-vibrator.

The fuel demand characteristic of the engine, however, is not straightforward. By way of example, the relation between the engine intake negative pressure and the amount of fuel to be supplied is not linear but is represented by a particular curve. Therefore, with the afore-mentioned conventional fuel control system the movable iron core associated with the multi-vibrator should have an extremely complicated configuration requiring very troublesome manufacturing steps. Besides, such a movable iron core gives rise to various problems in use such as mal-functioning due to external vibrations to deviate from the proper fuel demand characteristic, thus resulting in inferior reliability of the system.

Further, for engines having different fuel demand characteristics the pitch of the windings of the feedback transformers, dimensions of the diaphragm to convert engine intake negative pressure into mechani cal displacement and the configuration of the movable iron core coupled to the diaphragm should be basically changed. In other words, the above conventional system totally lacks in compatibility with engines of different ratings.

An example of the conventional fuel control system in US. Pat. No. 3,005,447 granted to Gunther Baumann et al. on Oct. 24, 1961. This patent comtemplates to obtain pulse signals each thereof having a pulse width corresponding to a valve opening time which determines the amount of fuel to be injected in the following way. In this patent, the output pulse current from a pulse signal generating circuit which is triggered by closing of a cam-driven contact is made to flow through the primary winding of a transformer contained in the circuit and the magnitude of a voltage induced in the secondary winding of the transformer is changed according to a variation in the mutual inductance caused by the displacement of a movable iron core of the transformer driven by a pressure gauge which is operated in response to intake manifold vacuum in an engine. The secondary induced voltage is rectified and applied to the base of a pre-stage transistor in the pulse signal generating circuit in series with a DC bias voltage to control the nonconductive period of the pre-stage transistor, which in turn controls the duration of the output pulse current.

I As seen from the above-described structure of the fuel control system of the US. Pat. No. 3,005,447, it is clear that such a system also contains all of the drawbacks of the conventional fuel control system such as described above.

SUMMARY OF THE INVENTION Anobject of the invention is to provide a fuel control system for internal combustion engines comprising a first signal generator to produce a voltage output corresponding to an operating parameter of the engine, and a signal processing circuit to modify the output of the first signal generator to introduce a non-linear character approximating the fuel demand characteristic of the engine by deriving from the output of the first signal generator a plurality of modified output components through respective circuits each providing an output pattern peculiar to a corresponding one of a plurality of subdivided parts of the engine fuel demand characteristic over the entire range of the involved engineoperating parameter and amplifying and adding together the respective derived voltage components through an amplifying means, whereby the pulse width of the pulse signal impressed on the fuel injection valve is varied in accordance with the voltage output of the signal processing circuit to meet the entire engine fuel demand characteristic.

According to the invention, an excellent advantage is featured in that-the pulse width of the pulse signal impressed on the fuel injection valve can be continually and exactly varied in accordance with a non-linear engine fuel demand characteristic over the entire range of the engine-operating parameter, thus enabling exact control over the amount of fuel supplied to the engine in accordance with the fuel demand characteristic of the engine with an extremely simple circuit construction. Another advantage featured by the invention is that it is possible to adopt the system according to the invention to various engines with different fuel demand characteristics by an extremely simple measure of merely varying the non-linear character of the nonlinear means producing a plurality of modified output components and the gains for the respective modified output components to suit a given engine fuel demand characteristic so as to exactly and faithfully control the amount of fuel injected in accordance with the fuel demand character of a particular engine. This means that the fuel control system according to the invention has an extremely simple requisite of merely varying the non-linear character of the non-linear circuit means and the gains involved in the aforesaid signal processing circuit for the compatibility with engines of different ratings.

Consequently, this invention provides an excellent fuel control system for internal combusion engines which eliminates the drawbacks of the conventional fuel control system including that which was disclosed by the U.S. Pat. No. 3,005,447 and has hereinbefore been described.

Another object of the invention is to provide a fuel control system for internal combustion engines, which further comprises two other signal generators, in addition to the first signal generator, to produce a voltage output corresponding to another operating parameter of the engine for addition to the signal processing circuit.

According to the second aspect of the invention, the pulse width of the pulse signal impressed on the fuel injection valve, that is, the amount of the fuel injected during the period of the pulse width, may be increased by an amount corresponding to the output voltage components for the output of the two signal generators. This is an excellent advantage in that a desired engine output torque may be produced when the engine is in a low temperature condition and/or accelerating condition, at which time the fuel supply should be increased.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a block diagram of a preferred embodiment of the fuel control system for internal combustion engines according to the invention.

FIG. 2 is a schematic circuit diagram, partly in block form, showing the principal part of the system of FIG.

FIGS. 3 to are graphs illustrating the operation of the system of FIG. 1.

FIG. 6 is a schematic circuit diagram, partly in block form, showing the principal part of a second embodiment of the system according to the invention.

FIG. 7 is a schematic circuit diagram similar to FIG. 6 showing a third embodiment of the system according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT temperature. It is actually a fuel increase signal generator to generate a fuel increase signal when the engine is in a low temperature condition, for instance when the engine temperature is below 40 C, so as to ensure smooth operation of the engine at low temperatures. Numeral 3 designates a third signal generator. It is also a fuel increase signal generator to generate a fuel increase signal on the basis of the action of a switch, which is closed when the engine intake negative pressure reaches a predetermined value, so as to increase the fuel supply particularly under the high-load and accelerating conditions of the engine for obtaining a desired engine output torque. The voltage outputs of the first signal generator l the second signal generator 2 and the third signal generator 3 are fed to a signal processing section 4, which produces output voltage e containing voltage components with respective gains to the corresponding inputs (to be described hereinafter in detail) Numeral 5 designates a switch constituting an ignition start signal generator. It is operated (opened and closed) synchronously with the fuel injection timing for the first cylinder of the four-cylinder engine, for example. In synchronism with the closure of the switch 5, a saw-tooth wave generator 6 generates a saw-tooth wave signal having a constant rise time. The fuel injection cycle time for the first cylinder is indicated at T. The saw-tooth wave voltage output of the saw-tooth wave generator 6 and the voltage output appearing at output terminal 4a of the signal processing section 4 are fed to a pulse signal generator 7, which produces a pulse signal with pulse width W corresponding to the output voltage at the output terminal 4a. The pulse sig nal from the pulse generator 7 is fed to a fuel injection valve drive 8, which energizes an electromagnetic solenoid (not shown) of a fuel injection valve 9 in response to the received pulse signal to drive the fuel injection valve 9 such that it is held in the operative or open position for a time interval equal to the pulse width W in each fuel injection cycle. The fuel injection valve 9 is provided in the first cylinder.

The switch 5, the saw-tooth wave generator 6, the pulse signal generator 7, the fuel injection valve drive 8 and the fuel injection valve 9 constitute a fuel injection subsystem for the first cylinder. Similar subsystems are also provided to the remaining second to fourth cylinders respectively, and the output voltages appearing at output terminals 4b, 4c and 4d are similarly added to the respective pulse signal generators.

The circuit construction of the signal processing sec tion 4 is shown in detail in FIG. 2. Referring to FIG. 2, numeral 10 designates an operational amplifier, numeral 11 a feedback resistor (with resistance R) to provide for the negative feedback from the output side to the input side of the operational amplifier 10, numerals 12 to 14 gain correction variable resistors connected to a common point at one end and to the earth at the other end, numeral 15 a gain adjustment resistor (with resistance R1) connected between a movable tap 12a of the variable resistor 12 and the input terminal of the operational amplifier 10, numeral 16 a gain correction constant-voltage diode connected between the movable tap 12a and the earth, numeral 17 a gain adjustment resistor with resistance R2 connected between a movable tap 13a of the variable resistor 13 and the input terminal of the operational amplifier l0, numeral 19 a gain correction constant-voltage diode connected between a movable tap 14a of the variable resistor 14 and a gain adjustment resistor (with resistance R3), which is in turn connected to the input terminal of the operational amplifier 10, numeral 20 a potential adjustment variable resistor with its movable tap 20a connected through a gain adjustment resistor 21 (with resistance R4) to the input terminal of the operational amplifier l0, numeral 22 a gain adjustment resistor (with reistance R5) connected between the output terminal of the second signal generator 2 and the input terminal of the operational amplifier 1t), and numeral 23 a gain adjustment resistor (with resistance R6) connected between the output terminal of the third signal generator 3 and the input terminal of the operational amplifier iii. The ratio of the components of the voltage output from the operational amplifier it) to the respective voltage outputs from the first to third signal generators l to 3 depends upon the ratio between the resistance R of the feedback resistor to each of the resistance R1, R2, R3, R4, R5 and R6 of the respective gain adjustment resistors l5, l7, 19, 21, 22 and 23.

To describe the operation of the fuel control system of the above construction according to the invention, it is assumed that the fuel demand characteristic of the engine is given by a curve A-B as shown in FIG. 3, where the ordinate represents the fuel amount Q to be injected in one fuel injection cycle and the abscissa represents the engine intake negative pressure P (mm Hg). The curve A-B represents the normal fuel demand characteristic without requiring an additional increase of fuel supplied. If the engine intake pressure P builds up beyond point P, with increase in the engine load, the fuel demand characteristic given by curve A-B is replaced with a fuel demand characteristic given by curve C-D, according to which the amount of fuel to be injected is increased by an amount 0, with respect to that according to the characteristic of curve A-B for the same intake negative pressure. When the absolute value of the intake negative pressure becomes lower than P,, the characteristic of curve A-B is recovered. Meanwhile, if the engine temperature is below, for instance, 40 C, the fuel supply is increased by an additional amount Q over the entire range of the engine intake negative pressure, thus replacing the fuel demand characteristics given by curves A-B and C-D with shifted fuel demand characteristics as represented by dashed curves A'B' and CD'. When the engine temperature exceeds, for instance, 40 C the characteristics of curves A-B and C-D become available again.

The fuel amount Q to be injected is proportional to the period, during which the fuel injection valve is held in the operative or open position, and which depends upon the output voltage e produced by the signal processing section 4. Thus, it is desirable that the output characteristics for the output voltage e produced by the signal processing section 4 are similar to the fuel demand characteristics of FIG. 3 for the fuel amount Q to be injected, as shown in FIG. 4. However, a voltage output characteristic identical with the curve A-B cannot be obtained over the entire range of the intake negative pressure in whatever way, so long as the output voltage produced by the negative pressure signal generator 1 is applied to the operational amplifier 10 only through the path of the gain correction variable resistor 13 and the gain adjustment resistor 17. Accordingly, the characteristic of curve A-B is approximated by a plurality of linear portions, for instance three portions A-F, F-E and E-B as shown in FIG. 4. In each portion, the relation between the voltage e and intake negative pressure is linear. The characteristic AF EB can be obtained by adding together a linear voltage varying in proportion at a certain proportionality constant to the intake negative pressure and a non-linear voltage,

d which varies in proportion to the intake negative pressure at a certain proportionality constant until the intake negative pressure reaches a predetermined value and at another proportionality constant when the predetermined value of the intake negative pressure is exceeded. To describe this point in further detail, a first voltage 'e',, which is proportional to the intake negative pressure, is obtained through the circuit of the gain correction variable resistor 13 and gain adjustment resistor 17, a second voltage e' which is constant when the intake negative pressure is less than F, and varies in proportion to the negative pressure when the negative pressure is greater than P is obtained through the circuit of the gain correction variable resistor I12 and gain correction constant-voltage diode 16, and a third voltage e;,, which is constant when the intake negative pressure is greater than P and varies in proportion to the negative pressure when the negative pressure is less than P is obtained through the circuit of the gain cor rection constant-voltage diode l8 and gain adjustment resistor 19. The relationship between the input voltage 2 to the operational amplifier l0 and the engine intake negative pressure -lP (mm Hg) is shown in FIG. 5. In the Figure, plot l-i-l represents the first voltage e plot GFl( represents the second voltage e';, and plot G-L represents the third voltage 2' Point E (corresponding to point E in FIG. 4) is determined by the breakdown voltage of the gain correction constant-voltage diode l8 and the resistance of the gain correction variable resistor l4, and point F (corresponding to point F in FIG. 4) is determined by the breakdown voltage of the gain correction constant-voltage diode l6 and the resistance 7 of the gain correction variable resistor 12. The first,

second and third input voltages e e' and e;; are respectively amplified by the ratios of R/R R/R, and R/R and then accumulated with a resultant output e through the operational amplifier M. It will be appreciated that by suitably setting the values of R ,R, and R the slope of the curve showing the output voltage e of the signal processing section 4 versus the engine intake negative pressure may be made to approximate the curve A-B over the entire pressure range. As the pulse width of the pulse output from the pulse signal generator 7 varies in proportion to the output voltage e from the operational amplifier lit), the amount of fuel supply to the engine can faithfully follow the fuel demand characteristic represented by the curve AB in FIG. 3. In FIG. 5, plot M-N represents a potential correction voltage (corresponding to a fourth voltage) given by the potential adjustment resistor 2d, plot O-R an output voltage (corresponding to a fifth voltage) from the temperature detection fuel increase signal generator 2, and plot S-T an output voltage (corresponding to a sixth voltage) from the pressure detection fuel increase sig nal generator 3. The potential correction voltage given by the potential adjustment resistor 20, which corresponds to the fourth input voltage (2",, with a gain determined by R/R is also fed together with the first, second and third input voltages e,, e: .and 2', to the operational amplifier 10, and it contributes a constant output voltage component to the output voltage of the operational amplifier it) over the entire pressure range, as indicated at e in FIG. 4.

When the engine temperature is below a predetermined value, for instance 40 C, the temperature detection fuel increase signal generator 2 provides an output voltage, which gives rise to the fifth input voltage e,

determined by R/Rs for impression together with the first to fourth input voltages e',, e' e' and e, on the operational amplifier 10. As a result, the curve A-B for the fuel demand characteristic is shifted to establish a new curve A'B over the entire range of the engine intake negative pressure. Thus, the output voltage e for the same negative pressure is increased by an amount e accounting for the fifth input voltage e This means an increase of the pulse width of the output pulse pro duced by the pulse signal generator 7 by an amount corresponding to the additional component e of the output voltage e from the operational amplifier 110. In this manner, the engine may be operated smoothly when the engine temperature is low, at which time an increased amount of fuel should be supplied to the engine.

When the engine intake pressure P exceeds the value P, in FIG. 3, the pressure detection fuel increase signal generator 3 produces an output voltage, which gives rise to the sixth input voltage e determined by R/R for impression together with the first to fourth input voltages 2' (2' e and e, on the operational amplifier 10. As a result, the curves A-F and OD for the fuel demand characteristic over a pressure range higher than P, are replaced with respective new curves A-F and C-D'. Thus, the output voltage e is increased by an amount e accounting for the sixth input voltage e This also means an increase of the pulse width of the output pulse produced by the pulse signal generator by an amount corresponding to the additional component e of the output voltage from the operational amplifier 10, In this manner, fuel supply may be increased to increase the engine output torque when the engine load is high and/or acceleration is applied to the engine.

The output characteristic of the signal processing section 4 may be patterned after various fuel demand characteristics of different engines by appropriately varying the resistance of the gain correction variable resistors l2, l3 and M, the breakdown voltage of the constant-voltage diodes l6 and 18, the resistance of the gain adjustment resistors l5, l7 and I9 and the resistance of the feedback resistor 11 such that the output voltage e of the operational amplifier l0 conforms to a given fuel demand characteristic. In some cases, the number of parallel current paths between the first signal generator 1 and the operational amplifier 10 may be increased or decreased to provide for a corresponding number of slopes approximating to the respective part of a given characteristic curve.

Although in the foregoing embodiment the first signal generator 1 is described as a negative pressure signal generator to generate electric signals corresponding to the engine intake suction pipe negative pressure, i.e., and electric signal corresponding to an engineoperating parameter, it may be replaced with a signal generator that produces an electric signal corresponding to a different engine-operating parameter such as engine speed, throttle opening and pressure in other parts of the engine. Also, the second and third signal generators are not limited to the temperature detection fuel increase signal generator 2 and the pressure detection fuel increase signal generator 3 as in the preceding embodiment, but other signal generators adopted to detect the conditions for increasing the fuel supply from the engine speed and throttle opening may be used as well. Further, the non-linear element for deriving from the output voltage of first control signal generator a plurality of voltages having non-linear relation with said voltages is not limited to the constant-voltage diodes l6 and 118, but other types of operational ampli fiers, transistors and combinations of these elements may also be used.

FIG. 6 shows second embodiment of the system, in which the voltage of the characteristic AFEB in FIG. 4 is obtained through operational amplifiers. In this Figure,pa1ts l, 2, 3, 4,11, 11a, 112, 12a, 13, 13a, 14-, 14a, l5, 17, 2t Zl, 22 and 23 are the same as the corresponding ones described earlier in connection with FIG. 4. Numerals 30 and 40 designate operational amplifiers, numerals 31 and 41 feedback resistors provided for the feedback from the output side to the input side of the respective operational amplifiers 3t and 40, and numerals 32 and 33 adjustment resistors determining the voltage level of one input to the respective operational amplifiers 3t) and 40. The other input to the operational amplifiers are obtained by correcting the voltage produced by the first signal generator in proportion to the intake negative pressure through respective gain correction variable resistors 12 and lid.

The operational amplifier 3d provides an output corresponding to the difference between the two inputs. When one of the input voltages is sufficiently large compared to the other input voltage determined by the adjustment resistor 32, the output voltage is not greater than the source voltage. Thus, the output voltage is constant when the intake negative pressure is greater than a predetermined value. In this way, the voltage appearing through the gain correction resistor 15 may have a characteristic GFK as shown in FIG. 5. In the operational emplifier 40, when one of the input voltages is sufficiently large compared to the other input voltage determined by the adjustment resistor 33, the output is reduced to the source voltage (which is zero in this case), so that the voltage appearing through the gain correction resistor 19 may have a characteristic GEK in FIG. 5.

FIG. '7 shows a third embodiment of the system according to the invention, in which the voltage of the characteristic AFEB in FIG. 4 is obtained. In FIG. 7, the same parts as those in FIG. 2 are designated by like reference numerals. Numeral 40 designates an n-p-n transistor, numeral 50 a p-n-p transistor, numerals 41 and 51 adjustment resistors determining the base potential on the respective transistors 40 and 50, numerals 42 and 52 are auxiliary resistors respectively determining the collector potential on the transistor 40 and the emitter potential on the transistor 50, and numerals 43 and 53 diodes. By presetting the resistance of the resistor 41 the collector-emitter current in the transistor 40 is determined to determine the voltage drop across the resistor 42. Similarly, by presetting the resistance of the resistor 51 the emitter-collector current in the transistor 5th to determine the voltage drop across the resistor 52.

When the intake negative pressure is greater than the predetermined value P,, the anode potential on the diode 4'13 is greater than the cathode potential thereon, that is voltage drop across the resistor 42, so that current flows through the diode 43. When the intake negative pressure becomes small enough, current ceases to flow from the anode to the cathode of the diode 43. In this way, the voltage appearing through the gain correction resistor 15 may have a characteristic GFK in FIG. 5. When the cathode side voltage on the diode 53,

9 that is, the intake negative pressure voltage, is great, the cathode potential on the diode 53, that is voltage drop across the resistor 52, is surpassed, so that current flows. When the intake negative pressure is redued,

current ceases. Thus, the voltage appearing across the gain correction resistor 19 may have a characteristic GEK in F IG. 5. The invention is not limited to the fourcylinder cylinder engine as in the above embodiment, but it may also be applied to the single-cylinder engine, two-cylinder engine, three-engine engine and engines having five or more cylinders.

As has been described in the foregoing, according to the first feature of the invention, with the provision of a first signal generator for producing a voltage output corresponding to an operating parameter of the engine, non-linear circuit means for modifying the output of the first signal generator so as to introduce a non-linear characteristic approximating the fuel demand characteristic of the engine by deriving from the output of the first signal generator a plurality of modified output voltages through respective non-linear circuit means,

each of the plurality of modified output voltages corresponding to each of aplurality of subdivided parts of the engine fuel demand characteristic over the entire range of the involved engine-operating parameter, and an operational amplifier which receives the plurality of modified output voltages and whose gains for the modified output voltages are adjusted according to the subdivided parts of the fuel demand characteristic of the engine to produce an output voltage covering to be the entire range of the fuel demand characteristic of the engine for varying the pulse width of a pulse signal impressed on the fuel injection valve, it is possible that the pulse width of the pulse signal impressed on the fuel injection valve can be continually and exactly varied in accordance with the engine fuel demand characteristic which is a non-linear function of an engine operating parameter over the entire range thereof. Thus, it is possible to exercise exact control of the amount of fuel supplied to the engine .in accordance with the fuel demand characteristic thereof with a circuit of extremely simple construction. Also, it is possible to apply the output voltage of the first signal generator to various engines with different fuel demand characteristics by an extremely simple measure of adjusting the nonlinear characteristic of the non-linear means and the gains of the operational amplifier for the respective modified output voltages to suit a given engine fuel demand characteristic of each of the engines so as to exactly and faithfully control the pulse width of the pulse signal to be impressed on the fuel injection valve, that is, the amount of the fuel to be injected which meets the fuel demand characteristic In other words, the fuel control system according to the invention has an extremely simple measure of merely varying the nonlinear characteristic of the non-linear circuit means and the gains of the operational amplifier employed to thereby obtain the compatibility with engines of different ratings.

Furthermore, according to the second feature of the invention with the provision of a second signal generator to detect the phenomenon requiring an increase of the fuel to be injected, and the voltage output of the second signal generator is added to the afore-said signal processing circuit, so that in addition to the effects obtainable according to the first feature of the invention it is also possible to increase the pulse width of the pulse signal impressed on the fuel injection valve, that is, the amount of the fuel injected, by an amount corresponding to the output voltage of the second signal generator, which is an excellent advantage in that a desired engine output torque may be produced when the engine is under a low temperature condition and/or an accelerating condition requiring a increase of the fuel supply.

We claim:

ll. In combination with a fuel injection system for internal combustion engines which :is provided with one or more fuel injection valves electromagnetically operated by a pulse signal changed by an output voltage representing fuel demand of the engine, produced based on at least one operating parameter of the engine, a fuel control system comprising:

a control signal generator to produce an output voltage, the value of said output voltage having a linear relationship with that of an operating parameter of the engine,

a signal processing circuit, including non-linear means and linear means, connected in circuit with said control signal generator, said non-linear means producing at least one first voltage, the value of which has a non-linear relationship with that of said first output voltage, said linear means producing at least one second voltage, the value of which has a linear relationship with that of said output voltage, and

an amplifier-adder connected in circuit with said signal processing circuit for amplifying and adding to gether said first voltage and second voltage so as to produce the output voltage to meet the fuel demand characteristics.

2. A fuel control system according to claim 1 further including another control signal generator for produc ing an output voltage when a value of another operating parameter of the engine satisfies a predetermined value, the value of said output voltage being constant, and said amplifier-adder being further connected in circuit with said another control signal generator and amplifying and adding together said first and second voltage and the output voltage of said another control signal generator to meet the fuel demand characteristics.

3. A fuel control system according to claim 1, wherein said non-linear means comprise constant voltage diodes and resistors.

4. A fuel injection control circuit for an internal combustion engine having at least one electromagnetically operated fuel injection valve which is held in an operative position by an electrical pulse signal having a duration in time which is varied as a function of the amplitude of a total output voltage, said amplitude of said total output voltage varying in accordance with fuel demand characteristics as a function of at least one operating parameter of the engine, comprising:

a control signal generating means for producing an output voltage which varies linearly with said at least one operating parameter of said engine,

a signal processing circuit, including non-linear signal producing means and linear signal producing means, connected to said first control signal generator, said non-linear means receiving said first output voltage and producing at least one first voltage which varies non-linearly with said first output voltage, said linear means producing at least one second voltage which varies linearly with said second gether said first voltage and second voltage so as to output voltage, and produce said total output voltage to meet said fuel adding and amplifying means connected to said sigdemand characteristics of said engine.

nal processing circuit for amplifying and adding to- 

1. In combination with a fuel injection system for internal combustion engines which is provided with one or more fuel injection valves electromagnetically operated by a pulse signal changed by an output voltage representing fuel demand of the engine, produced based on at least one operating parameter of the engine, a fuel control system comprising: a control signal generator to produce an output voltage, the value of said output voltage having a linear relationship with that of an operating parameter of the engine, a signal processing circuit, including non-linear means and linear means, connected in circuit with said control signal generator, said non-linear means producing at least one first voltage, the value of which has a non-linear relationship with that of said first output voltage, said linear means producing at least one second voltage, the value of which has a linear relationship with that of said output voltage, and an amplifier-adder connected in circuit with said signal processing circuit for amplifying and adding together said first voltage and second voltage so as to produce the output voltage to meet the fuel demand characteristics.
 2. A fuel control system according to claim 1 further including another control signal generator for producing an output voltage when a value of another operating parameter of the engine satisfies a predetermined value, the value of said output voltage being constant, and said amplifier-adder being further connected in circuit with said another control signal generator and amplifying and adding together said first and second voltage and the output voltage of said another control signal generator to meeT the fuel demand characteristics.
 3. A fuel control system according to claim 1, wherein said non-linear means comprise constant voltage diodes and resistors.
 4. A fuel injection control circuit for an internal combustion engine having at least one electromagnetically operated fuel injection valve which is held in an operative position by an electrical pulse signal having a duration in time which is varied as a function of the amplitude of a total output voltage, said amplitude of said total output voltage varying in accordance with fuel demand characteristics as a function of at least one operating parameter of the engine, comprising: a control signal generating means for producing an output voltage which varies linearly with said at least one operating parameter of said engine, a signal processing circuit, including non-linear signal producing means and linear signal producing means, connected to said first control signal generator, said non-linear means receiving said first output voltage and producing at least one first voltage which varies non-linearly with said first output voltage, said linear means producing at least one second voltage which varies linearly with said second output voltage, and adding and amplifying means connected to said signal processing circuit for amplifying and adding together said first voltage and second voltage so as to produce said total output voltage to meet said fuel demand characteristics of said engine. 